Congqin Ning

Wide-range hydrogen sensing with Nb-doped TiO2 nanotubes

Anatase-type titania nanotubes doped with Nb element were fabricated through an anodization of Ti35Nb alloy substrate and further annealing at 450 °C. Hydrogen sensitivity of the Nb-doped TiO(2) nanotubes at room temperature was investigated through exposure of the nanotube samples to different hydrogen atmospheres. At room temperature, the Nb-doped nanotubes demonstrated a good sensitivity for wide-range detection of both dilute and high-concentration hydrogen atmospheres ranging from 50 ppm to 2% H(2). The Nb-doped nanotubes also presented remarkable reversibility and repeatability as well as a quick response to the hydrogen atmosphere. The Nb-doped titania nanotubes have great advantages as robust and wide-range hydrogen sensors operating at room temperature.

Anodic fabrication and bioactivity of Nb-doped TiO2 nanotubes

We report anodic formation of Ti-Nb-O nanotubes on top of a Ti35Nb alloy, and in vitro bioactivity and stem cell response of the anodic nanotubes. It was found that the amorphous Ti-Nb-O nanotubes presented a significantly enhanced in vitro bioactivity (in simulated body fluids) compared to those of undoped TiO2 nanotubes and porous Ti-Nb-O without nanotubular structure. Similar to undoped TiO2 nanotubes, the Ti-Nb-O nanotubes also promote mesenchymal stem cell adhesion and fast formation of extracellular matrix (ECM) materials. The above findings make it possible to further explore the biological properties, such as cell proliferation and drug delivery, of a variety of Ti-alloy-based oxide nanotubes.

p-Type hydrogen sensing with Al- and V-doped TiO2 nanostructures

Doping with other elements is one of the efficient ways to modify the physical and chemical properties of TiO2 nanomaterials. In the present work, anatase TiO2 nanofilms doped with Al and V elements were fabricated through anodic oxidation of Ti6Al4V alloy and further annealing treatment. Hydrogen sensing behavior of the crystallized Ti-Al-V-O nanofilms at various working temperatures was investigated through exposure to 1,000 ppm H2. Different from n-type hydrogen sensing characteristics of undoped TiO2 nanotubes, the Al- and V-doped nanofilms presented a p-type hydrogen sensing behavior by showing increased resistance upon exposure to the hydrogen-containing atmosphere. The Ti-Al-V-O nanofilm annealed at 450°C was mainly composed of anatase phase, which was sensitive to hydrogen-containing atmosphere only at elevated temperatures. Annealing of the Ti-Al-V-O nanofilm at 550°C could increase the content of anatase phase in the oxide nanofilm and thus resulted in a good sensitivity and resistance recovery at both room temperature and elevated temperatures. The TiO2 nanofilms doped with Al and V elements shows great potential for use as a robust semiconducting hydrogen sensor.

Thermal stability and in vitro bioactivity of Ti–Al–V–O nanostructures fabricated on Ti6Al4V alloy

This work investigates the thermal stability and in vitro bioactivity of Ti-Al-V-O nanostructures grown on Ti6Al4V alloy through an anodization method. After anodization of the two-phase Ti6Al4V alloy, there were two different kinds of Ti-Al-V-O nanostructure (nanotube arrays grown in the alpha-phase region and irregular nanopores grown in the beta-phase region) that formed on the surface of the alloy. It was found that the Ti-Al-V-O nanotubes can withstand a high temperature of 675 degrees C in air without collapse, whereas the irregular Ti-Al-V-O nanopores presented a lower thermal stability. In vitro simulated body fluid (SBF) testing of heat-treated nanostructures indicated that a quick apatite formation on these nanostructures occurred after only several hours of sample immersion in the SBF.

Biological properties of Ti-Nb-Zr-O nanostructures grown on Ti35Nb5Zr alloy

Surface modification of low modulus implant alloys with oxide nanostructures is one of the important ways to achieve favorable biological behaviors. In the present work, amorphous Ti-Nb-Zr-O nanostructures were grown on a peak-aged Ti35Nb5Zr alloy through anodization. Biological properties of the Ti-Nb-Zr-O nanostructures were investigated through in vitro bioactivity testings, stem cell interactions, and drug release experiments. The Ti-Nb-Zr-O nanostructures demonstrated a good capability of inducing apatite formation after immersion in simulated body fluids (SBFs). Drug delivery experiment based on gentamicin and the Ti-Nb-Zr-O nanostructures indicated that a high drug loading content could result in a prolonged release process and a higher quantity of drug residues in the oxide nanostructures after drug release. Quick stem cell adhesion and spreading, as well as fast formation of extracellular matrix materials on the surfaces of the Ti-Nb-Zr-O nanostructures, were found. These findings make it possible to further explore the biomedical applications of the Ti-Nb-Zr-O nanostructure modified alloys especially clinical operation of orthopaedics by utilizing the nanostructures-based drug-release system.

Fabrication and hydrogen sensing properties of doped titania nanotubes

Titania nanotubes have been widely used in gas sensing applications such as hydrogen sensors. Doping titania nanotubes with other elements are expected to provide tunable band-gap and thus favorable hydrogen sensing properties. In this work, Nb, Zr-doped titania nanotube arrays in crystallized states were fabricated on alloy substrates through anodization and heat-treatment. And doped nanotube sensors were assembled on PCB. Corresponding anodization and sensor fabrication processes were investigated and hydrogen sensing properties of the nanotube sensors were tested in hydrogen atmosphere. Experimental results indicated that the content of Zr had a great impact on the growth, thermal stability and hydrogen sensing property of regular nanotube arrays. The Nb-doped nanotubes demonstrated a good hydrogen sensing performance.